1. Field of the Invention
The invention concerns a data receiver device for reception of a broadcast electromagnetic signal containing correction data for a global navigation satellite system (GNSS), especially for a vehicle, motor vehicle, aircraft or seafaring vehicle. The invention also concerns a method of navigation by means of a global navigation satellite system (GNSS), in which differential GNSS data (DGNSS data) are used to correct the GNSS data.
2. Prior Art
A world-wide satellite navigation system, which is designated the global positioning system (GPS) or global navigation satellite system (GLONASS) was built up by the military in the U.S.A. and the former USSR. The GPS and GLONASS systems and further developments of these satellite navigation systems are included in the term, "global navigation satellite system (GNSS)". The precise signals are generally encoded so that an operator obtains an accuracy of about 3 m only by direct use of the method.
Only an uncoded signal with continuously changing artificially poorer position data is available for the civilian user. The resulting poorer accuracy of 100 m is however sufficient for many users. A method has already been suggested with which an accuracy of 3 m is attainable. An additional GNSS receiver is installed at an exactly known position and used as a reference station. The received GNSS position data and the known actual position data are compared with each other in the reference station. The difference is transmitted as correction data to mobile stations by means of a radio signal containing the correction data. All GNSS receivers in the reception area of this radio signal can accordingly correct their positions determined by means of the GNSS data on this basis.
The actual position of the reference station is determined as accurately as possible on the basis of the civilian GNSS signal. This position determined using a carrier phase measurement is very accurate. After a calibration stage permanent correction values are measured and transmitted to the mobile reception apparatus. The mobile reception apparatus receives the GNSS signal automatically and uses the input correction data in order to determine its position. Subsequently the position data is made available for further processing. It can be output on a display screen and/or used for vehicle navigation. This method is called differential GNSS or is abbreviated DGNSS.
Position locating ability is becoming ever more significant with the increasing use of traffic telematic devices and navigation devices in motor vehicles. Position locating receivers are coming into greater use for the NAVASTAR global positioning system (GPS) and the GNSS system, which allow a three-dimensional position determination by transit time measurements to at least four GNSS satellites. As high as possible a positioning accuracy and availability is required of these receivers in the sense of a high system integrity.
A widely used method for increasing accuracy of the GNSS position data is provided by the above-described differential GNSS (DGNSS). In DGNSS correction values from the received satellites are computed by a stationary reference station having a known position and are transmitted in real time by means of a telemetric link to the mobile user. All correlated errors (i.e. the constant error in the region covered by the reference station) can be eliminated by including these correction values in the navigation method in the mobile receiver and thus the accuracy of the GNSS position determination by the mobile user is considerably increased.
Up to now the DGNSS method is predominantly used for geodetic purposes, in which the reference station was operated locally by the user or a users group. A DGNSS service for all of Europe, which would be required for application of the DGNSS method in mass use, has not been available up to now.
Correction data from different DGNSS servers however will be offered in the near future over different transmission channels based on the expected mass use in land, air and water traffic. First attempts have shown that the individual DGNSS services may provide different quality service with different availability because of the different transmission methods (frequency, phase or amplitude modulation) and because of the different transmission frequencies (long wave, medium wave, ultrashort wave).
However it is disadvantageous that the navigation devices based on GNSS use only one source for the radio signal containing the DGNSS data or only a single DGNSS service or only one reference station. Since these services broadcast only locally but do not overlap, GNSS navigation refined by means of DGNSS is available only in certain limited local areas.